Updated

Soldiers from the Army's 101st Airborne Division (search) found another trailer in northern Iraq that experts believe was a mobile biological weapons laboratory (search), the division's commander said Tuesday.

The troops found the trailer Friday at al-Kindi (search), the largest former missile research facility in Iraq, said Maj. Gen. David Petraeus, commander of the 101st. The trailer is "close to identical" to another found last month in the same area that U.S. officials believe was a mobile germ weapons workshop, Petraeus told Pentagon reporters in a two-way video link from his headquarters in Mosul.

Some equipment from the latest trailer had been taken by looters, and there were indications such as unfinished welding that the apparatus was incomplete, Petraeus said. He said a military weapons expert told him "there's a reasonable degree of certainty this is a mobile biological agent production trailer."

President Bush said he waged war against Saddam Hussein's government to eliminate Iraq's biological and chemical weapons programs. So far, no weapons of mass destruction have been found in Iraq, despite visits to more than 100 suspect sites by U.S. investigators.

Pentagon officials have pointed to the discovery of the first trailer -- seized at a checkpoint near Mosul by Kurdish forces on April 19 -- as possible proof that Iraq indeed had active programs to produce weapons of mass destruction. Saddam and other officials said Iraq destroyed all its chemical and biological weapons in the 1990s.

In a United Nations presentation before the war, Secretary of State Colin Powell said Iraq had built several mobile weapons laboratories to conceal production of biological and chemical weapons. Pentagon officials say both trailers found in northern Iraq appear to match the descriptions from Iraqi sources Powell used in that presentation.

Serial numbers on both trailers indicated they were made as a set, Petraeus said. The first one found had a serial number of 1 and a construction date of 2002, while the second had the serial number 2 and a construction date of 2003, he said.

The second trailer soon will be taken to Baghdad International Airport, where military experts are examining the first trailer, Petraeus said.

Soldiers from the 101st Airborne found several sites where officials thought at first there were chemical or biological weapons, only to find through further testing that there were no weapons of mass destruction there. Petraeus said he did not know whether Iraq had destroyed all of its banned weapons in the 1990s as it claimed, destroyed them just before the war or had them very well hidden.

"I think the explanation's still out there to be found," he said.